The optical recording media are widely used, generally due to the superior characteristics such as large recording capacities, noncontact recording or reproduction, and the like. In the write-once optical discs such as WORM, CD-R, DVD+R, and the like, recording is carried out by focusing the laser light on a minute area of the recording layer to change properties of the optical recording layer, while reproduction is performed based on a difference in intensities of light reflected from the recorded area and non-recorded area.
In the optical recording layer of an optical recording medium represented by an optical disc, organic dyes are used because they easily form the optical recording layers. Especially, cyanine-based compounds are being examined because of having high sensitivity and corresponding to high speed recording.
Presently, in the optical discs mentioned above, the wavelength of semiconductor laser light used for recording and reproduction is between 750 and 830 nm for CD-R and between 620 and 690 nm for DVD-R. Further, a still higher density optical disc corresponding to laser light with a wavelength of 600 nm or shorter has been developed. Pentamethine cyanine compounds which correspond to these optical discs are reported, for example, in Patent Documents 1 to 11 and the like.
However, the pentamethine cyanine compounds have problems in thermal decomposition characteristics. For high speed recording, thermal interference is required to be small and, for this purpose, optical recording materials with low decomposition temperature and steep thermal decomposition characteristics are suitable. However, each of the cyanine compounds reported in the Documents did not have sufficient characteristics in this regard.    Patent Document 1: Japanese Patent Laid-Open Publication No. S59-55795    Patent Document 2: Japanese Patent Laid-Open Publication No. H05-173282    Patent Document 3: Japanese Patent Laid-Open Publication No. H11-53761    Patent Document 4: Japanese Patent Laid-Open Publication No. H11-227331    Patent Document 5: Japanese Patent Laid-Open Publication No. H11-277904    Patent Document 6: Japanese Patent Laid-Open Publication No. H11-34499    Patent Document 7: Japanese Patent Laid-Open Publication No. 2000-108510    Patent Document 8: Japanese Patent Laid-Open Publication No. 2000-289335    Patent Document 9: Japanese Patent Application Laid-Open No. 2001-506933    Patent Document 10: Japanese Patent Laid-Open Publication No. 2003-231359    Patent Document 11: Japanese Patent Laid-Open Publication No. 2006-312710